For example, in Patent Document 1 there is disclosed a Fabry-Perot fiber laser.
In order to cause the Fabry-Perot fiber laser to operate as a pulsed laser by a Q-switching operation, an optical switch that instantaneously changes optical transmittance is arranged inside a resonator. Such an optical switch includes an LN modulator, an acousto-optic modulator (AOM), and a variable optical attenuator (VOA) such as a mechanical shutter.
In the pulsed laser, it is important to shorten the pulse width in order to increase workability. A Q-switched laser generates pulses having a pulse width of the order of from 10 neck to 100 nsec. In the Q-switched fiber laser, because the resonator length tends to be long, it is difficult to generate a short pulse, as compared with a solid-state laser.
In a Q-switched pulse oscillator configured in this manner, as a solution to shorten the pulse width, there can be mentioned: (1) a method of increasing the circulation gain of the oscillator by increasing feedback; (2) a method of increasing the circulation gain of the oscillator by increasing the gain of the amplifier; and (3) a method of shortening the resonator length.
However, in the method of increasing the circulation gain of the oscillator by increasing feedback, there is a limitation in the effect of shortening the pulse width.
In the method of increasing the circulation gain of the oscillator by increasing the gain of the amplifier, if the gain of the amplifier is increased, the pulse width is shortened monotonically. However, to do this, an excitation device needs to be high-powered, leading to a cost increase.
In the method of shortening the resonator length, as the resonator length becomes shorter, the pulse width becomes shorter. A fiber resonator consists of optical components and its pig-tail fibers. In the fiber resonator, each component has pig-tail fibers of a certain length, and hence, the total length of the pig-tail fibers depends on the number of parts. Therefore, if the number of parts increases, the total pig-tail fiber length becomes long, thereby increasing the resonator length.
Moreover, with Q-switching, the number of optical parts increases by the number of optical switches. Therefore, connection points between the parts increase, causing an increase in production man-hours and an increase in interconnection loss.
[Prior Art Document]
[Patent Document 1] Japanese Patent No. 3219415